Times are hard for the international criminal court. It is nine years since it was established with notions of ending impunity for "unimaginable atrocities that deeply shock the conscience of humanity". The arrest in Libya last week of four members of the court's defence team, who were visiting Muammar Gaddafi's son, Saif al-Islam, marked a new low in the court's history.

But with only one conviction in its history, an exclusively African caseload, and relations with other African states also at breaking point, the court's reputation leaves much to be desired.

Into the fray steps Fatou Bensouda, the Gambian who on Friday becomes chief prosecutor – the second in the court's history and the first African woman.

Her most immediate task will be to resolve the standoff with Libya, amid concern for the welfare of the ICC envoys after the Libyan government said they had been placed in "preventive detention" in prison for 45 days during investigations into alleged threats to Libya's national security.

Alexander Khodakov, of Russia, Esteban Peralta Losilla, of Spain, Lebanese Helene Assaf and Australian Melinda Taylor were arrested after meeting Gaddafi, who is in detention and has been indicted by the ICC. They were held at an unknown location before being moved to a prison.

Human rights groups have strongly condemned the move by Libya, which they say violates international law and the immunity given to ICC staff, and claim that they have not had access to legal advice. "The detention of the four staff members of the international criminal court is unacceptable," said Mark Ellis, executive director of the International Bar Association. "Defence rights are essential for any meaningful judicial proceedings at the national and international levels and should be adhered to in the proceedings of Saif al-Islam Gaddafi's trial."

The detention comes after months of tension between the court and the Libyan government over where the toppled dictator's son and former spy chief, Abdullah al-Senussi should stand trial.

On the surface, it is hard to see how Bensouda, a public prosecutor and former attorney general of the Gambia, could be equipped to turn around the fortunes of the ICC, which is based in The Hague. Her country – with a population of only 1.7 million – is notorious as one of west Africa's last dictatorships, with opposition to President Yahya Jammeh's 18-year regime suppressed.

Yet among those who follow – and frequently criticise – the ICC, there is a surprising degree of faith in Bensouda's leadership, and a view that she has remained unscathed despite her professional relationships with Jammeh and the deeply unpopular outgoing chief prosecutor, the Argentinian Luis Moreno-Ocampo.

"I feel positive about Fatou's tenure as chief prosecutor," said Chidi Odinkalu, chairman of the Nigeria national human rights commission. "Will she wave a magic wand and cure all the difficulties that exist at the ICC at the moment? No. Can she bring positive disposition over time to transforming the polluted atmosphere in which the institution has been operating in Africa? Absolutely."

A full-blown crisis in relations between the courts and the African Union was triggered by the decision to issue an arrest warrant for the Sudanese president Omar al-Bashir in 2009 for genocide, crimes against humanity and war crimes for his role in the situation in Darfur. After Moreno-Ocampo ignored an AU warning that attempting to arrest al-Bashir could undermine peace talks in Sudan, African member states retaliated by flouting the warrant, and welcoming al-Bashir into their jurisdictions.

Bensouda's popularity stems in no small part from the fact that she is not Moreno-Ocampo. "Fatou brings a different set of skills and temperament from her predecessor, and that is a positive thing" said Odinkalu. "She has a pretty difficult job given the state of relations between the ICC and African states – things are quite honestly abysmal."

Despite her close professional relationship with Moreno-Ocampo, she remains a popular choice. "A lot of people have said that Fatou has been a yes man – someone that just followed or went along with LMO's policies, but she has made it clear that while it is important to consolidate the gains made over the past nine years, there are things that could be improved," said Alpha Sesay, a Sierra Leonean lawyer based in The Hague for the Open Society Justice Initiative. "I do really accept that things will be different under her."

"Fatou is someone who is ready to listen and provide answers. You can sense that this is a different regime from the past, that she wants to listen, and to have a dialogue," Sesay added.

Bensouda is also – crucially – African. "She qualified here in Nigeria but really made her name in the Gambia," said Odinkalu. "She did have a reputation as a principled but also sensitive and sensible leader of the bar and chief law officer of the country. She even came out of serving her stint at the justice ministry with her reputation intact … in fact she is one of the very few who has."

Bensouda was born in the Gambia in 1961 to a polygamous Muslim family, and raised by her father's two wives. She had more than a dozen siblings. It was in this family setting that Bensouda said she developed her sense of justice. Her father – who died from diabetes when she was young – provided equally for both sides of his family and instilled a sense of fairness in his children. "We did not have this unfortunate rivalry that sometimes happens in polygamous families, and we were all very good to one another," she has said.

After studying at the University of Ife in Nigeria, being called to the Nigerian bar, and attending the UN's International Maritime Law Institute in Malta, Bensouda spent 20 years climbing the ranks of Gambian public legal office, as director of public prosecutions, solicitor general and attorney general.

"Prosecuting is Fatou's area," said Amie Bensouda, a former solicitor general who has known Bensouda since school and served as her superior in public office and colleague in private practice. "She is a very able prosecutor, she is highly respected and independent.

"Fatou tried some other areas of work in her career … she worked at a bank at one point and worked with me in chambers on some civil matters. But I don't think she enjoyed it. The area of law that she is comfortable with is prosecution. Her career progression was fast but it was also meritorious."

Bensouda's international career began when she started work as a legal adviser at the international criminal tribunal for Rwanda, the Arusha-based hybrid tribunal that combined international and Rwandan law to try those deemed most responsible for the 1994 genocide. In 2004 she joined the ICC as deputy prosecutor working under Moreno-Ocampo.

Although she has defended her former boss, since her appointment was made public in December, Bensouda has set out new priorities for the court, including improving the quality and efficiency of investigations, ensuring violence against children and sexual and gender crimes are reflected in future charges, and improving the court's relationship with Africa.

"There is no question that the AU [African Union] is warming up to Fatou. How much further things go is going to depend a lot on her diplomatic skills," said Sesay. "And in that, she is going to be completely different from Moreno-Ocampo."

Many challenges remain. The first is to get Arab countries to sign up to the Rome Statute, which established the ICC – Tunisia stands alone as the only Arab nation to belong to the court. Libya, where acts committed by pro-Gaddafi forces during last year's uprising are before the court, has acted with aggressive defiance of its investigations, refusing to surrender Gaddafi.

Perhaps the most important task for Bensouda, international lawyers say, will be to change the court's approach towards victims. "People have the mistaken impression that it is just heads of state, motivated by their own self interest, who have criticised the ICC – it's not," said Odinkalu. "The first alarm bells were sounded by victims' communities – they have a sense of being used, abused, dumped and not cared for."

"Fatou's accession gives ICC an opportunity to redeem relationships with victims' communities, show them that it is capable of caring – she inherits a situation in which the ability to be deeply nuance is needed and if she has those skills, which she seems to, that will be an asset," said Odinkalu.

Bensouda insists that for her, helping victims is at the centre of what international criminal justice is really about. "That's where I get my inspiration and my pride," she said.

Potted profile

Born: Gambia, 31 January 1961

Career: Called to bar in Nigeria, qualified in international maritime law, public prosecutor in the Gambia's attorney general's office, DPP, solicitor general, attorney general and minister of justice. Legal adviser to the international criminal tribunal for Rwanda. Appointed deputy chief prosecutor at the international criminal court in 2004.

High point: Invited to attend African union summit in July, signalling thawing of relations between the AU and ICC strained under Luis Moreno-Ocampo.

Low point: The Gambian government using the courts to suppress freedom of press shortly after Bensouda's tenure as attorney general and justice minister.

What she says: "I am an African and I am very proud of that … But I think it is not because I am an African that I was chosen for this position. I think my track record speaks for myself … I have been endorsed by the African Union, but I am a prosecutor for 121 states parties and this is what I intend to be until the end of my mandate."

What they say: "The 'helpful' thing about Bensouda is that merit and political expediency go hand in hand. She is a woman, she is African and she is considered to be highly capable." Rebecca Lowe, International Bar Association